Regidized porous material and method

ABSTRACT

A small particle porous material rigid wicking structure and a method of fabrication therefor are disclosed. The structure is fabricated from micron sized uniformly graded and shaped powder particles using a viscous slurry starting material and a one step or multiple step heating sequence. Details describing typical heat pipe and battery component uses of the porous material are included. Superior liquid conveying performance is achieved with the described porous material.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

CROSS REFERENCE TO RELATED APPLICATIONS

The following patent applications are somewhat related and have the samefile date. Some of these applications also include one or more of thepresent application inventors as a named inventor thereof and are alsocommonly assigned to the Government of the United States represented bythe Secretary of the Air Force. Each of these applications is alsohereby incorporated by reference herein. The present application(designated by an *) is included in this list for clarity andcompleteness of the record.

    ______________________________________                                        Number                                                                        Identification                                                                          Title                                                               ______________________________________                                        AF 18277A Electrical Battery Cell Wicking Structure                                     and Method                                                          AF 18277B (*) Rigidized Porous Material and Method                            AF 17953  Alkali and Halogen Rechargeable Cell with                                     Reactant Recombination                                              AF 18278  A Method of Manufacturing Heat Pipe Wicks                                     and Arteries                                                        AF 18279  A Method of Manufacturing Heat Pipe Wicks                           AF 19413  Unidirectional Heat Pipe and Wick                                   ______________________________________                                    

BACKGROUND OF THE INVENTION

This invention relates to porous media useful in the surface tensiontransfer of liquids and to the fabrication of porous media structures.The achieved porous medium is useful in a variety of technical artsincluding the herein referred to electrical battery cell and heat pipearts.

The transportation of liquid materials to elevated or otherwise liquidreservoir separated locations without the use of moving parts is auseful concept that is often employed in, for example, the electricalbattery cell, machinery lubrication, combustion and other chemicalreaction and the heat transfer arts. In each of these uses, there isneed for relatively small quantities of a liquid material to be presentin physical locations that are distal from the reservoir of liquidmaterial and in conditions which are preferably free of pumps or othermechanically operated fluid displacement arrangements.

In certain of such uses, there is also present a need for effectivetransfer of thermal energy and for the accomplishment of such transferin situations which may include any of the liquid, gaseous, and solidphysical states of materials. Porous media, especially the porous mediaof the present invention, are useful in accomplishing energy transferinvolving the flow and especially the recirculating flow of liquideffluents as in a heat pipe.

The patent art includes a number of examples of porous media structuresand their fabrication and is indicative of the modern evolution of thisart. Included in this art is the patent of K. P. Staudhammer et al, U.S.Pat. No. 3,762,011 which concerns the fabrication of a wick for use in aheat pipe. The Staudhammer patent contemplates wick preparation by theapplication of a slurry of high thermal conductivity particles andorganic binder and organic solvent to the surface of a heat pipe. Thisapplication is followed by evaporation of the solvent and utilization ofbinder material surface tension properties to draw the high conductivityparticles together in a bonded and compacted condition. The achievementof compacted material is followed by curing of the binder. In theStaudhammer wick structure, cured binder material is used to hold thewick together in an integral condition and to retain the wick structurein predetermined relationship with the attending heat pipe surfaces.This cured binder arrangement contrasts with the particle retentionarrangement of the present invention. The Staudhammer particle size,particles of mesh size between 50 and 200 microns, and the use of anorganic binder and its participation as a particle densifying mechanismalso distinguish the Staudhammer structure from the present invention.

The prior patent activity also includes the patent of W. Fischer et al.,U.S. Pat. No. 3,840,069 which concerns a sintered heat pipe capillarystructure having a distribution of both fine pores and coarse pores. Inthe Fischer et al. structure, the wick pores are formed in a sinteredmetal powder structure by either removing one metal component of thepowder grains through a chemical reaction or by an alternate oxidizingand reduction chemical treatment of the metal powder structure or by theuse of metal powder having grins of different size in the powdercomposition.

The patent of E. A. Dancy et al, U.S. Pat. No. 4,082,863, concerns thefabrication of a ceramic heat pipe wherein is disposed a capillary layerof metal oxide ceramic material used to conduct the heat transfer fluid.In the Dancy et al. patent, a substrate member is coated with an aqueousslurry of metal oxide ceramic having a maximum particle size of about 44microns and the slurry is covered with a granular ceramic materialhaving a particle size in the range of 250 to 500 microns. According toa further aspect of the Dancy et al patent slurry material is also drawnup between particles and this fabrication is followed by firing of thecoated surface at a temperature effecting bonded of the ceramic layer.

The Dancy et al patent is particularly directed toward the fabricationof ceramic heat pipes made from dielectric materials. The Dancy et alheat pipe contemplates use of a variety of fabrication materialsincluding metal, glass and alumina ceramic materials with the workingfluid including liquefied gases, liquid metal, hydrocarbons,fluorocarbons, ammonia, water, acetone, methanol, ethanol, the freoncompounds, and other fabricated working fluids.

The Dancy et al heat pipe also contemplates use of sintered metalstructures in order to achieve good heat transfer between the heat pipecapillary maze and the heat pipe container, see column 2, line 35-39.Silica is said to be an essential constituent of the mixture used infabricating the Dancy et al structure because of its large melting pointrange and its resulting action as a glue between substrate and porouscapillary material, see column 3, lines 57. In the Dancy et alstructure, the fine particles of slurry mixture are used in order toachieve gluing action between substrate and larger particles of theslurry mixture, see column 4, lines 33-40. The ceramic substrate, use ofoxide powder materials, larger particle size and gluing action of theslurry material inter alia distinguish the Dancy et al apparatus fromthat of the present invention.

The patent of G. Y. Eastman, U.S. Pat. No. 4,274,479, also concerns aheat pipe capillary wick structure, a structure fabricated from sinteredmetal--and disposed with longitudinal grooves on its interior surface.The Eastman wick grooves provide longitudinal capillary pumping whilethe sintered wick provides a high capillary pressure to fill the groovesand assure effective circumferential distribution of the heat transferliquid. The Eastman patent also contemplates use of a viscous pastematerial for forming a wick structure, see column 4, lines 50-55. Atcolumn 4, line 16, the Eastman patent also describes the use of ahydrogen atmosphere and temperatures in the 900° C. range forfabricating a copper powder based wick structure.

Other known patents of possible interest as background with respect tothe present invention include U.S. Pat. Nos. 4,207,209; 4,307,164;4,372,823; and 4,665,049.

None of these patent examples or their combination, however, suggest theporous material structure of superior liquid transporting capability andheat transfer capability of the present invention.

SUMMARY OF THE INVENTION

In the present invention, a rigidized porous material member, whichemploys particles of small and substantially equal size physicaldimensions is achieved. The resulting structure is usable in a varietyof technical arts involving surface tension liquid transportation.

It is an object of the invention, therefore, to provide an improvedsurface tension liquid transportation apparatus and a fabricationsequence therefor.

It is another object of the invention to provide a liquid wickingapparatus which employs metallic particles of small physical size in itsfabrication.

It is another object of the invention to provide a liquid effluentwicking apparatus which can be fabricated conveniently and at low cost.

It is another object of the invention to provide a porous material thatis useful in a combined liquid effluent transportation and heat transferutilization.

It is another object of the invention to provide a porous materialfabrication sequence in which the application of heat energyaccomplishes both viscous binder dissipation/disintegration andcapillary wick cavity formation.

It is another object of the invention to provide a fabrication sequencein which a heat energy application also accomplishes sintering fusion ofparticles into a unitary rigid structure.

It is another object of the invention to provide a wicking structurethat is particularly adapted to the transportation of liquid metaleffluent.

It is another object of the invention to provide a porous materialstructure that is useful in conducting fluid effluent within a heatpipe.

It is another object of the invention to provide a rigidized particlestructure that is usable in the nucleate boiling mode of heat transfer.

It is another object of the invention to provide a metal particlewicking arrangement that accomplishes significantly improved wickingaction in comparison with conventional wick arrangements.

Additional objects and features of the invention will be understood fromthe following description and the accompanying drawings.

These and other objects of the invention are achieved by coating asubstrate member with a liquid suspension of finely divided metalparticles in an organic binder, adding additional dry metallic particlepowder to the surface of the liquid suspension coating, drying themetallic particle coating, and heat treating the metallic particlecoating in a reducing gas atmosphere held above the decompositiontemperature of the organic binder material and below the melting pointof the metal particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a portion of an electrical battery cell that is providedwith a porous material wicking member in accordance with the presentinvention.

FIG. 2 shows a microphotograph of the FIG. 1 porous material.

FIG. 3 shows a method for fabricating a porous material wicking memberof the FIG. 1 and FIG. 2 type.

DETAILED DESCRIPTION

FIG. 1 in the drawings shows a rigidized porous material capillary wickstructure that is disposed on one element of an electrical battery cell.The FIG. 1 wick serves the purpose of improving the contact or wettingaction of one battery reactant material with the substrate member 102when the FIG. 1 structure is immersed in liquefied battery reactantmaterials. A detailed description of the battery art usage of the hereindescribed porous material is contained in one of the above identifiedco-pending patent applications, "Electrical Battery Cell WickingStructure and Method". Since the electrical battery cell of varyingtypes is but one of the possible uses of the present invention, and theother uses recited early in the background of the invention topic aboveare also merely examples of the uses that will occur to persons skilledin the art, the present disclosure will make repeated references to twoof the possible of these uses--the electrical battery cell and a heatpipe liquid conveyance with the understanding that such references areexemplary and not limiting in nature.

The battery cell element of FIG. 1 includes the substrate member 102which is in actuality a solid electrolyte member for use in, forexample, a sodium and sulfur electrical battery cell. The substratemember 102 is provided with a flange 104 for capturing the substrate orelectrolyte member within the battery cell. The substrate or electrolytemember is shown to be cut away as indicated at 106 in order that theinterior portion thereof be visible.

On the exterior surface 108 of the substrate member 102 is disposed awicking material coating 100 which is more fully described below andwhich serves to enhance the reactant material wetting or contact withthe exterior surface 108 of the substrate member 102. The wickingmaterial coating 100 is especially useful in electrical battery cellembodiments such as the sodium sulfur cell wherein the liquid sodiumreactant material has minimal wetting affinity for materials, such asfor the preferred beta double prime alumina, used for fabricating thesubstrate member 102. Because of this poor wetting affinity, it hasbecome common practice in fabricating battery cells of this type to usephysical structure elements and other complexities that are disposedadjacent the electrolyte or substrate 102 member in order to promotetravel and intimate contact or wetting by the sodium reactant material.

In other arrangements of the wicking structure according to theinvention, the wicking material 100 may be disposed on a different typeand shape of substrate member or alternately may be fabricated as astand-alone or separate structure that is not associated with asubstrate member. Certain modifications of the wicking memberfabrication sequence herein described are required when the wickingmaterial coating is disposed in this stand-alone configuration. Thefabrication sequence and its modifications are described in connectionwith FIG. 3 below.

A wicking material coating may, of course, be disposed on the internalsurface 110 of a substrate--electrolyte member 102 in FIG. 1, when suchdisposition is required by the employed battery cell reactantconfiguration; such internally disposed wicking structures are alsoappropriate for use in the heat pipe uses of the invention. For use in abattery cell environment a shown in FIG. 1, the wicking material coating100 may be fabricated with a thickness in the range of 0.02 inch to 0.08inch or 0.5 to 2.0 millimeters; with other thicknesses especially forother utilizations of the wicking material, being possible.

FIG. 2 in the drawings shows a porous metallic material structure inaccordance with the invention such as the FIG. 1 wicking material100--as the porous metallic material appears following its subjection toa physical fracture event. The FIG. 2 microphotograph is descriptive ofone face of the fracture at a magnification of 1,000 times. A series ofexternally located arrow pairs and individual arrows, each of which isnumbered, indicate text described internal features of the FIG. 2 porousmaterial; the features thusly identified in FIG. 2 are to the bestdegree possible, of sufficient prominence and size as to be ofreproducible during electrostatic or other copying to the FIG. 2microphotograph. This numbered arrow reference arrangement is selectedin view of the glossy and non-markable nature of the microphotographicprint submitted in the application for Letters Patent.

In FIG. 2, the fracture surface nature of the microphotograph and themagnification ratio of the image are indicated by the arrow 200 at thetop of the figure. The two arrows, 202 and 204, in FIG. 2 togetherindicate the horizontal and vertical coordinates of one easilyidentified component particle of the FIG. 2 material. As indicated bythis particle, the porous or wicking material of the present inventionis preferably fabricated of particles having a single radius dimension,that is, fabricated from spherically shaped particles having a uniformparticle size. When fabricated as a rigidized metallic powder structure,the particle identified by the arrows 202 and 204 is of some three tofive microns diameter and may be, for example, composed of metallicnickel such as the nickel in powdered form that is available fromInternational Nickel Corporation under the identifying name of type 255MOND metal powder. Alternate types of nickel powder include the typeNI228 electronic grade powder of three microns nominal size, the typeNI227 plasma spray powder of 150 microns and larger size, and the typeNI172 plasma spray powder of 200 mesh or about 75 microns particle size,all of which are available in 99.9% purities from Atlantic EquipmentEngineers Inc. of Bergenfield, N. J. The larger particle size powders,of course, result in larger conduction paths in the FIG. 2 type ofstructure and may be desirable in some uses of theinvention--particularly when effluents of greater viscosity are to beconveyed via the porous material.

Two particularly well-defined, close to the fracture surface, and highlyilluminated ridge structures are indicated by the arrows 210 and 211 inFIG. 2. The slope of the arrows 210 and 211 also indicates the generalcourse of the designated ridge in the FIG. 2 microphotograph. As isillustrated by the structure of the ridges 210 and 211, the FIG. 2porous or wicking material is comprised of a very large number, aplethora, of individual particles which are randomly disposed andattached to each other to define a random maze or convoluted array ofcapillary passages--passages which are readily utilized as conductionpaths by a liquid effluent material. The arrow pairs 206, 208 and 212,214 indicate the vertical and horizontal locations of two suchconvoluted paths which extend into the depth of the FIG. 2microphotograph.

As is described in FIG. 3 formation of the FIG. 1 and FIG. 2 porous orwicking material structure is preferably accomplished with a suspensionof particles in a viscous binder solution, followed by drivinq off ordissipation of the liquid and organic components of the binder materialduring an elevated temperature exposure. During dissipation of theliquid and organic components of the binder material surface tension andother coagulation forces bring the wicking material particles into apacked and closely adjacent physical relationship. The further elevatedtemperatures of a sintering operation fuses the packed individualparticles into the structure shown in FIGS. 1 and 2.

The wicking performance of the FIG. 1 and FIG. 2 porous material hasbeen found to be superior to the performance of more conventional wickarrangements. By way of example, a wick in accordance with the FIG. 1and FIG. 2 structure, when fabricated from the above identified 255nickel powder of substantially circular shaped particles and particlesizes in the range of three to five microns, when immersed in liquidsodium at a temperature of 328° C., is found capable of generating acolumn of liquid sodium which easily and rapidly reaches 9 inches inheight. Since this liquid sodium height is attained in a period of fiveto ten minutes, and occurs in accordance with a linear height versustime relationship (the Table 1 data corresponds to a straight line witha correlation factor of 0.9935), it is clearly indicative ofsignificantly greater possible wicking heights achievable with theporous material of the invention in either the battery or heat pipe orother use environments.

The rate of travel of the liquid sodium in the herein described wickingmaterial is in accordance with Table 1 below.

                  TABLE 1                                                         ______________________________________                                        Distance     Time                                                             ______________________________________                                        1 inch        7 seconds                                                       2 inches     20 seconds                                                       3 inches     40 seconds                                                       4 inches     49 seconds                                                       5 inches     60 seconds                                                       6 inches     77 seconds                                                       7 inches     94 seconds                                                       8 inches     120 seconds                                                      9 inches     135 seconds                                                      ______________________________________                                    

The possibility of dissimilar velocities or non-linear velocity ofliquid travel in opposite travel directions in the porous material ofthe present invention is also notable and offers a potentially usefularrangement for accomplishing specialized tasks as is described in theabove identified co-pending patent application, "Unidirectional HeatPipe".

Materials other than the above identified metal and metals other thanthe above-identified nickel are, of course, usable in fabricatingwicking structures in accordance with the invention. Materials such asstainless steel, copper, aluminum and iron are included in this list.Suitable adjustments for the material temperatures involved in thefabrication steps of FIG. 3 and FIG. 4 below herein are, of course,required during the use of these alternate metals and non-metallicmaterials.

As is also indicated in the above preferred to co-pending patentapplication of myself and three other colleagues, the application titled"Battery Cell Wicking Structure and Method", uses of the presentinvention involving heat energy flow are enhanced by the use of metallicor other high thermal conductivity powder in the porous material.

The presence of a mild chemical reaction between the wick liquideffluent and the particles of the herein described porous material mayalso be advantageous under some operating conditions. A reaction of thisnature is believed present in the above-described liquid sodium andnickel particle wicking arrangement and is believed to contribute to thedescribed superior wicking performance. This reaction is to the extentof 0.004 to 0.20 parts per million at a temperature in the range of 200°C. to 600° C. as is described in the "Electrical Battery Cell WickingStructure and Method", co-pending patent application from the above listof co-pending patent applications. The presence of such a reaction, ofcourse, is accompanied by a resulting reaction product contamination ofthe wicked liquid effluent or the porous material or both but in view ofthe limited reaction occurring, this effect is of minor significance. Afinite operating life for the wicking structure is also implied by thisreaction, however, other failure mechanisms are usually more significantin determining the end of a cell practical operating life. The glass andalumina based materials identified above are immune from participationin reactions of this type with most wicked materials.

FIG. 3 in the drawings shows a sequence of processing steps 300 by whichthe FIG. 1 and FIG. 2 illustrated porous material wick structure can befabricated. As indicated at 302 in FIG. 3, this processing sequence maycommence with a substrate shaped in some predetermined configuration.When such a substrate is used, its surface is prepared for reception ofthe wicking material by way of an etching or similar process as isindicated at 304 in FIG. 3. When the substrate material is alumina or asimilar material, a surface preparation etch can be accomplished byexposing the alumina to water at a temperature of 200° C. for a periodof 1 to 5 minutes or in a more rapid manner by exposure of the aluminasurface to an alkali hydroxide in, for example, an aqueous based 1.0normal concentration of sodium hydroxide. Exposure times of less thanone minute at a temperature of 200° C. are found to be satisfactory forthe alkali etching sequence. In the case of alternate substrate members,surface preparation may be accomplished by an etch which uses selectedreactant materials or by mechanical abrasion.

Coating of the substrate surface with a metallic particle slurry isindicated in the step 306 of FIG. 3. The method of accomplishing thiscoating is dependent upon the shape of the substrate member being coatedand upon the internal surface or external surface nature of the coatedarea. For the external surface coating arrangement shown in FIG. 1, thecoating of step 306 may be accomplished by brush application of thesmall particle slurry directly onto the substrate surface withsupplementing, in order to achieve greater wicking member thickness,accomplished by sprinkling additional metallic particle dry powder overthe slurry wetted surface as is indicated in step 308 in FIG. 3. Slurryapplication by spraying, dipping, flowing, or even a mixing of the drypowder with a solvent material in the presence of the substrate memberare all within contemplation of the invention.

The slurry applied to the substrate member may consist of a solvent suchas, for example, an alcohol, preferably alcohol of the ethanol type orwater that is added to the dry powder of the wicking material. Alsoincluded in the slurry is a dissolved organic binder material such asMethocel binder that is sold in powder form by Dow Corning Corporationand a water soluble resin of, for example, the Polyox type that is soldby Union Carbide Corporation.

Preparation of the slurry with the metal particles and the combinedorganic binder material using an alcohol or water solvent or othersolvents is described by the manufacturers and typically involvesproportions as follows:

200 grams of Type 255 Nickel Powder

2 grams of Polyox

2 grams of Methocel

240 grams of water

The slurry is prepared by mixing the dry ingredients and then addingwater with continuous stirring.

If a shape compatible with rotational spinning is involved, spinning atabout 1500 RPM may be accomplished for two hours or until the slurry isdry. After spinning or in lieu thereof a baking at 500° C. for one houris used following by a one hour sit and a 5-minute bake at 1000° C. Foruse in the brush application sequence identified above, it is preferablethat the organic binder material have a room temperature viscosity thatis in the range of 500 centistokes to 1000 centistokes with a value nearthe 750 centistokes center of this range being preferred. ACannon-Fenske opaque (reverse flow) viscosimeter may be used for suchViscosity measurements. It is desirable for the wicking member particlesto be somewhat movable in the viscous pre-dry or pre-bake slurry duringand following the particle to substrate application in order that theagglomeration of particles represented in FIG. 2 be possible duringsolvent dissipation and binder material disintegration and dissipation.

In instances where the wicking material is to be fabricated in a standalone or non-substrate associated form, the slurry material may beconfined to a mold or predetermined container shape during its green oruncured condition and may also be fabricated in successive layers ofwicking material with each layer acting as a substrate for a successivelayer.

The green wicking member, that is, the uncured slurry comprising awicking member and resulting from particle application in steps 306 and308 in FIG. 3 is dried as is indicated by the block 310 in FIG. 3 usinga vacuum drying, air drying or other controlled atmosphere dryingprocess and using temperatures in the range of 500° C. and drying timesin the range of one hour. This drying, of course, removes a majorportion of the solvent material present in the green wicking. During itsinitial phases this drying also encourages particle movement under theinfluence of surface tension and adhesion between the binder coatedparticles to provide a structure of the type shown in FIG. 2.

The green wicking member is fired in a reducing gas atmosphere furnaceat temperatures which are preferably in the 900° C. to 1000° C. rangefor a period of about of five minutes following the attainment of stabletemperature; this firing is indicated by the sintering step at 310 inthe FIG. 3 sequence. The indicated 5 minute time and 900° C. to 1000° C.temperature values for the sintering step 312 in FIG. 3 are typical ofvalues that are satisfactory for the identified nickel powder slurry andsuch values result in individual particles having the degree of meltedfusion shown in FIG. 2. Longer times and higher temperatures for thesintering step provide greater degrees of article melting and result ina more "stringy" or less well-defined individual particle appearance forthe achieved porous material. A large variety of particle fusion andparticle appearance variations is, therefore, available in the porousmaterial by way of selecting the times and temperatures used in thesintering step of block 312 in accordance with the experience of personsskilled in the heat treatment arts.

Although porous material having the general appearance shown in FIG. 2is satisfactory for some uses of the invention including use for theliquid sodium wicking in an electrical battery cell, other employmentsof the invention involving different effluent materials and differenteffluent viscosities may be enhanced through he use of different timesand temperatures in the step 312. Similarly, with the selection ofdifferent metals or different non-metallic materials for the porousmaterial, a different set of time and temperature values will beoptimum--temperatures in excess of the 900° C. to 1000° C. value will,for example, be desirable in the case of ceramic materials.

For a nickel porous structure, the atmosphere in the firing or sinteringfurnace is preferably made to be reducing in nature by the addition ofhydrogen in the concentration range of 4 to 5% or by the addition ofother reducing gases as are known in the art. Otherwise, the furnace hasan inert atmosphere of helium, argon, nitrogen, or similar gases. Areducing gas atmosphere is desirable in the furnace since hydrogen andother such reducing gases combine with oxygen or oxide layers on themetallic particles at elevated temperatures thereby cleansing themetallic surfaces and allowing intimate sintering fusion of theparticles to occur.

Some reducing gases are capable of attacking some substrate materialsthat may be used for supporting the porous structure in its greenstate--especially at temperatures just below the above indicated 90020C. to 1000° C. range. In view of this tendency, the cooldown of a porousnickel sintered metal member as is indicated at 314 in FIG. 3 ispreferably arranged to occur in an inert gas atmosphere, that is thereducing qas component of the sintering atmosphere is removed while theworkpiece is yet at the elevated sintering temperature. Regardless ofthis refinement, however, the cooldown sequence is preferablyaccomplished according to a predetermined temperature profile whichgenerally includes a temperature reduction rate of 200° C. per hour.Following the sintering step of block 314 wicking member thicknesses inthe range of eighty thousandths of an inch are desired in the nickelparticle and alumina substrate use of the invention.

Generally, the need for a tradeoff compromise is recognized between thedesirability of small liquid transmitting passages in a porousmaterial--in order to achieve high capillary pressures--and thedesirability of large liquid transmitting passages capable of conductinghigher volumes of fluid through the porous material. The small passageand high capillary pressure end of this selection scale are desirablefor achieving large effluent delivery heights while the large liquidtransmitting passage end of this selection scale is desirable toaccomplish, for example, greater heat transmission in a heat pipe or thegreater reactant communication need for large current delivery in abattery cell. Since large working fluid passages inherently have lowcapillary pressure characteristics such a compromise is clearlyrequired. One arrangement of this compromise involves the use ofarteries of somewhat large diameter to transmit fluid to a region of useand capillaries of smaller diameter to distribute the artery transmittedfluid within the region of use. This arrangement is employed in theexample below.

When used in a heat pipe of the below indicated physical size and otherparameters, a porous nickel structure according to the inventionprovides heat transfer characteristics as are also discussed below. Theheat pipe of this discussion is contained in a circular tube of 0.875inch, 2.2225 centimeters, inside diameter of type 304 stainless steelhaving 0.0625 inch wall thickness and 8.875 inch length with end plugsof 0.25 inch thickness--so that an effective length of 8.375 inches or21.27 centimeters is achieved. A 0.375 inch inside diameter fill tube isreceived in one end plug. Eight fluid communication arteries of 0.075inch diameter are dispersed uniformly around the porous wick structure.

Methanol working fluid of a volume of 26.3 cubic centimeters isintroduced into the heat pipe. The 26.3 cm³ volume substantially fillsthe heat pipe since a porous material porosity of eighty-seven percentis measured and an extra ten percent of working fluid volume is added toaccommodate condensate trapped in the fill tube.

The theoretical heat transfer limits incurred in a heat pipe use of theporous material of the invention--that is the working fluid physicslimits are identified as the sonic limit, the entrainment limit, theboiling limit and the capillary limit. These limits for the workingenvelope of a heat pipe are known in the art and are described, forexample, in the textbook "Heat Pipe Theory and Practice" written by S.W. Chi and published by Hemisphere Publishing Company of Washington,D.C. In the described heat pipe structure, the first two of theselimiting considerations support a relatively large quantity of heattransmission and are, therefore, of minimal porous material describinginterest. Of the latter two limiting phenomenon, the boiling limit Qb ismost significant by an order of magnitude in determining the maximumheat transfer capability of the described heat pipe when the assumedvalues of the working envelope limit equation variables are used. As isknown to persons skilled in the art, however, the determination ofaccurate values for some limit equation variables is usuallyaccomplished with some difficulty.

More specifically for the porous material of the invention used in aheat pipe, the Sonic Limit, Qs,max is predicted by the relationship:##EQU1##

In similar fashion, the Entrainment Limit is predicted by therelationship ##EQU2##

The Boiling Limit is predicted by the relationship; ##EQU3##

The Capillary Limit is predicted by the relationship: ##EQU4##

In most heat pipe arrangements, the Capillary Limit Q_(c) defines theoperating region boundary of greatest concern.

The heat transfer ability of the described heat pipe having nickelparticle porous material according to the invention is in the range ofone hundred twenty-five watts. This value is subject to improvement withoptimization.

While the apparatus and method herein described constitute a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus or method, and thatchanges may be made therein without departing from the scope of theinvention, which is defined in the appended claims.

I claim:
 1. A rigidized particle liquid effluent wicking membercomprising the combination of: a plethora of substantially sphericallyshaped and equally sized metallic nickel particles of three to fivemicrons nominal size disposed into a randomly joined particle rigidphysical array of predetermined external configuration; said array alsoincluding viscous binder determined capillary maze means having bindervoided contiguous capillary passages randomly dispersed through thearray for conveying liquid effluent material surrounding said particlesand throughout said wicking member.
 2. The wicking member of claim 1wherein said particles are joined together by both heat treated binderand sintered fusion bond between adjacent particles.
 3. The wickingmember of claim 2 wherein said capillary maze means includes heattreated binder material having temperature immunity.
 4. A wicking memberformed by the process of:coating one surface of a substrate member witha wet slurry of finely divided metal particles and organic binder;dusting the wet surface of said slurry coating with a coating thickeningadditional layer of said finely divided metal particles; drying thethickened metallic particle coating until rigidized into a substrateattached wicking member; driving off the liquid and organic bindercomponents of said wicking member wet slurry in a first elevatedtemperature atmosphere; sintering the wicking member at a second highertemperature.